/*
 * Copyright (c) 2003-2010, Live Media Pty. Ltd.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met:
 *
 *  1. Redistributions of source code must retain the above copyright notice, this list of
 *     conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright notice, this list of
 *     conditions and the following disclaimer in the documentation and/or other materials
 *     provided with the distribution.
 *  3. Neither the name of Live Media nor the names of its contributors may be used to endorse
 *     or promote products derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.colony.concurrent;

/**
 *  List is a basic linked list designed to act as a Queue.  Single direction
 *  traversal only.
 */
public class List
{

   private ListItem _front;
   private ListItem _back;
   private int _count;


   List()
   {
      _front = null;
      _back = null;
      _count = 0;
   }


   /**
    *  returns true if the List is empty.
    */

   boolean isEmpty()
   {
      synchronized( this )
      {
         if ( _front == null ) return true;
         return false;
      }
   }

   /**
    *  Add an object to the list.
    */

   void add( Object o )
   {
      synchronized( this )
      {
         ListItem l = new ListItem( o );

         if ( isEmpty() )
         {
            _front = l;
            _back = l;
         }
         else
         {
            _back.next = l;
            _back = l;
         }
         _count++;
      }
   }

   /**
    *  Remove an Object from the list using FIFO method.  Returns null is list is empty.
    */

   Object remove()
   {
      synchronized( this )
      {
         if ( isEmpty() == true )
            return null;
  
         ListItem l = _front;
         _front = _front.next;
         _count--;
         return l.item;
      }
   }     


   public int count()
   {
      synchronized( this )
      {
          return _count;
      }      
   }

   private class ListItem
   {
      public Object item;
      public ListItem next;

      ListItem( Object o )
      {
         item = o;
      }
   }

}
